On the first 5 quizzes of his physics class, Christopher got an average score of 86. What does he need on the next quiz to have an overall average of 88?
Explanation: Let his score on the next quiz be $x$ The sum of all of his scores is then $5 \cdot 86 + x$ The same sum must also be equal to $6 \cdot 88$ Solve: $x = 6 \cdot 88 - 5 \cdot 86 = 98$.